With the ever present drive to miniaturize modern technology, one great challenge facing engineers is developing devices of ever smaller proportions that can operate reliably with high precision, in sometimes harsh environments. It may be desirable to provide such devices with small scale moving components such as actuators, position detectors, vibrations detectors, flow sensors, or detectors for small surface defects having displacements on the sub-millimeter or even sub-micrometer scale. However, it is difficult to equip such components with sensor systems that reliably measure such small displacements at these scales. It is also particularly difficult to do so with a sensor system that exhibits high signal to noise ratio across an entire range of displacement. Flow sensors and other devices for measuring fluids also present the additional engineering challenge of inhibiting exposure of the sensor and associated electrical circuitry to potentially corrosive fluids; therefore, there must be a physical barrier such as a non-permeable membrane between any sensors and the fluid media.
Additionally, flow sensors may be coupled to flow control valves. In this application, the flow sensor may be used to control the flow of fluid through a flow control valve. One well known type of flow control is mass flow control. In mass flow control, the flow sensor measures the mass flow of a fluid through a flow passage and then adjusts an associated flow control valve on the flow passage to cause the measured mass flow rate to trend toward a set point. Thus, in mass flow control, the mass flow rate of fluid through the system is constantly measured and used to adjust the flow control valve and thus to adjust the mass flow rate. It will be appreciated that mass flow control is subject to overshooting and undershooting the set point for the mass flow rate. To minimize the magnitude of the overshoots and undershoots, mass flow control systems are typically configured to adjust the flow control valve position slowly and/or incrementally. Therefore, one drawback to mass flow control systems is that they are generally slow to respond to sudden changes in the measured mass flow rate of the system. In circumstances in which nearly instantaneous change in flow rate is desired, mass flow control systems can lack sufficient responsiveness.